Mirrors for various uses are known in the art. For example, see U.S. Pat. Nos. 5,923,464 and 4,309,075 (all hereby incorporated herein by reference). Mirrors are also known for use in projection televisions and other suitable applications. In the projection television context, see for example U.S. Pat. Nos. 6,275,272, 5,669,681 and 5,896,236 (all hereby incorporated herein by reference).
One type of mirror is a second or back surface mirror (most common), while another type of mirror is a first or front surface mirror (less common). Back surface mirrors typically include a glass substrate with a reflective coating on a back surface thereof (i.e., not on the front surface which is first hit by incoming light). Incoming light passes through the glass substrate before being reflected by the coating in a second surface mirror. Thus, reflected light passes through the glass substrate twice in back or second surface mirrors; once before being reflected and again after being reflected on its way to a viewer. In certain instances, passing through the glass substrate twice can create ambiguity in directional reflection and imperfect reflections may sometimes result. Mirrors such as bathroom mirrors, bedroom mirrors, and architectural mirrors are typically back or second surface mirrors so that the glass substrate can be used to protect the reflective coating provided on the rear surface thereof.
In applications where more accurate reflections are desired, front (or first) surface mirrors (FSMs) are often used. In front/first surface mirrors, a reflective coating is provided on the front surface of the glass substrate so that incoming light is reflected by the coating before it passes through the glass substrate. Since the light to be reflected does not have to pass through the glass substrate in first surface mirrors (in contrast to rear surface mirrors), first surface mirrors generally have higher reflectance than do rear surface mirrors, and no or less double reflected image. Example front surface mirrors (or first surface mirrors) are disclosed in U.S. Pat. Nos. 6,783,253, 5,923,464 and 4,780,372 (all incorporated herein by reference).
It has been proposed to use a metallic chromium (Cr) reflective layer in a first surface mirror. In particular, the proposed mirror includes a layer of metallic Cr located directly on and contacting a glass substrate. Unfortunately, such first surface mirrors with a structure of glass/Cr suffer from pinhole related problems. In particular, such a mirror structure is susceptible to pinhole formation in the metallic Cr layer, especially as the Cr layer thickness increases in applications where lower transmission (e.g., 0.5% visible transmission) are desired. Light tends to leak through such pinholes making large numbers of them especially undesirable in mirror applications where reflectance (not transmission) of light is desired.
It will be apparent from the above that there exists a need in the art for a first/front surface mirror, or other type of mirror, that is less susceptible to significant amounts of pinhole formations.